This invention relates generally to improvements in shaft bearings and related bearing mounting arrangements particularly for use in turbochargers and the like. More specifically, this invention relates to an improved turbocharger bearing assembly having relatively simple and easily assembled means for axially retaining a pair of journal bearings, while providing enhanced oil flow over and about journal bearing surfaces.
Turbochargers in general are well known in the art for supplying relatively high pressure air, commonly referred to as charge air, to the intake manifold of an internal combustion engine such as a reciprocating piston engine of the type commonly used to power automobiles, trucks, buses and the like. Typically, the turbocharger comprises a turbine housing connected for receiving exhaust gases expelled from the engine and configured to guide those exhaust gases into driving communication with a rotatable turbine wheel. The turbine wheel is carried on a rotatable shaft which extends through a center housing having shaft bearing components and supports a compressor impeller within a compressor housing. The turbine wheel thus rotatably drives the impeller, which in turn draws ambient air into the compressor housing for compression and discharge in the form of charge air for supply to the intake manifold of the engine. In this regard, turbochargers function to supply the engine with an increased mass flow of air to permit engine operation at substantially increased levels of performance and power output.
The rotating shaft in a modern turbocharger is normally designed for relatively high rotational speeds, such as on the order of 100,000 rpm or more. Such rotational speeds require the use of precision bearing components together with an effective system of bearing lubrication. In this regard, lubricating oil is commonly pumped under pressure- through a center housing for contact with turbocharger journal and thrust bearings to prevent excessive bearing heating and wear.
In the past, significant design effort has been directed toward improvements in turbocharger bearing design. Such design efforts have been particularly directed toward reducing wear and/or audible noise attributable primarily to high frequency radial shaft excursions caused by unbalanced rotating components. See, for example, the turbocharger journal bearings described in U.S. Pat. Nos. 3,058,787 and 4,427,309. However, these prior bearing designs have generally relied upon conventional retaining rings to axially position and retain sleeve type journal bearings on a turbocharger shaft. Unfortunately, the use of such retaining rings requires precision ring grooves to be formed in the turbocharger center housing, and further requires tedious assembly steps to insure proper placement and seating of the retaining rings.
Alternative turbocharger bearing arrangements have been proposed in attempts to eliminate the use of conventional retaining rings and the complex manufacturing steps associated therewith. For example, cylindrical bearing spacers have been suggested for installation axially between a pair of journal bearings. The opposite ends of the bearing spacers are intended to cooperate with enlarged shoulders or other thrust surfaces on the turbocharger to achieve precision axial retention of the journal bearings, for example, U.S. Pat. Nos. 4,358,253 and 4,364,717. See also German Publication No. 2,061,393. However, these prior concepts utilizing a central bearing spacer have not provided adequate oil flow over and about the inner and outer diameter surfaces of the journal bearings. Accordingly, although the central bearing spacer has permitted elimination of standard retaining rings, relatively premature journal bearing failure attributable to inadequate lubrication has occurred. Such bearing spacer arrangements, therefore, have not achieved any significant commercial acceptance.
The present invention overcomes the problems and disadvantages encountered in the prior art by providing an improved turbocharger bearing assembly of the type having a central bearing spacer for axially locating journal bearing components. The present invention provides a particular combination of journal bearing and thrust surface geometries for promoting adequate flow of lubricating oil over and about the journal bearing surfaces.